The Biggest Loser's veteran trainer Bob Harper has admitted he was "stunned" when he saw Rachel Frederickson walk out during last week's finale having shed an additional 45 pounds in just six weeks.

"What people don't understand is, when the contestants leave to go home... they're in charge of themselves," Harper said on the Rachael Ray Show in an episode that will be aired Feb. 13. "So I had not seen her until that night, and so when she walked out, I was just kind of like, whoa. And I've been on the show since the beginning."

He also added: "I was stunned. That would be the word. I mean, we've never had a contestant come in at 105 pounds."

Frederickson, 24, started the show at 260 pounds. When she left as a finalist she weighed 150 pounds and later lost 45 more. That has brought a wave of criticism for the show as being irresponsible and setting up contestants to develop eating disorders so they can lose the most weight the fastest.

"I think that there's a don't-ask-don't-tell policy going on," said Brenda Weber, associate professor of gender studies at Indiana University, in an interview with NPR. "I mean, one of the things that people I've talked to who've participated on The Biggest Loser in particular have shared with me is that the way the show positions time on the show is inaccurate and so the weigh-ins are not weekly, which means you can amass bigger numbers in what looks like a smaller amount of time. And then ... once they're off the ranch, all bets are off and they do everything they possibly can do in order to bring those numbers down."

Frederickson has said that before the weigh-in, she had been taking "maybe three, four (exercise) classes a day," including Zumba and spin. "I even went home over the holidays to Minnesota and I went running outside," she added.

"We're not comfortable commenting on Rachel's journey because we weren't her trainers and weren't given an opportunity to work with her at any point. Any questions about the contestants on The Biggest Loser should be directed to the show's producers."

For her part, Frederickson is happy with her new body, saying on Tuesday's finale: "I just love myself, and I am embracing it," and that her "goals are to be healthy and strong."